The multidrug resistance (MDR1) P-glyco-protein (Pgp) is a 140-180 kDa plasma membrane protein which was first identified as an ATP-dependent transporter for efflux of structurally diverse chemotherapeutic agents from tumor cells. MDR1 Pgp is also expressed in normal tissues, such as the liver, kidney, and adrenal, where its physio-logical function(s) and substrate(s) are not known. Recent studies suggest that MDR1 Pgp may be involved in intracellular trafficking of cholesterol, possibly mediated through vesicle formation or acidification. The focus of this proposal is to characterize the functional significance and mechanism of action of MDR1 Pgp for intracellular transport of cholesterol. Involvement of MDR1 Pgp is sterol trafficking will be tested in cells that express different levels of Pgp. Pharmacologic approaches, using compounds which inhibit MDR1 Pgp or acidification of vesicles, and genetic approaches, using antisense methods to reduce expression of Pgp and infection with recombinant viruses expressing mutant rab proteins, will be employed. Through the training program based on this research proposal, the clinician-scientist will increase his knowledge in basic sciences of molecular and cell biology, pharmacology, and lipid metabolism. Research in the poorly understood process of intra-cellular transport of cholesterol will allow the clinician-scientist to learn and integrate laboratory methods used for recombinant DNA, assessment of vesicular transport, quantification of lipids, and transport kinetics and inhibition. The ultimate goals of this proposal are to use didactic course work, workshops, and the expertise of established investigators at Washington University School of Medicine to train the clinician-scientist in basic science research, study the role of MDR1 Pgp in trafficking of cholesterol, and facilitate the development of the clinician-scientist as an independent investigator. (End of abstract)